The generant which is employed in automotive airbag installations may be any of several types. The charge may be made up of loose pellets, of stacked wafers, or may comprise one or more single extruded grains. In a passenger-side airbag installation, the generant charge is normally installed in a cylindrical ignition can and is surrounded by a cylindrical filter which may be made, for example, from materials such as steel wool to prevent sparks or particles of hot material from entering the airbag. It is necessary to preload the generant charge in order to cushion it from damage due to shock and to prevent looseness that would permit movement under vibration. An additional reason for preloading is the difference in thermal expansion between the aluminum and steel portions of the installation. The ignition chamber is normally aluminum while its internal components are primarily steel. As a result, the aluminum, which has greater heat expansion, is the first to be affected. Although temperature changes during normal operation are usually slow and have little effect on the length differential, the assembly must undergo testing requirements wherein the temperature change conditions are more exaggerated.
Most commonly, preload is accomplished by the use of foamed rubberized silicone pads such as disclosed, for example, in U.S. Pat. No. 4,846,368 of Goetz. The problem with using this material is that it is subject to off-gassing and burning.
Another problem with prior art preload assemblies is that the preload mechanism is not normally a part of the filter/generant assembly, thereby resulting in a more complex installation than would be desired.
Accordingly it is a primary object of the present invention to provide a generant preload which is metallic to preclude off-gassing and burning. Another object is to provide such a preload which is integral with the filter to simplify assembly. Other objects, features and advantages will become apparent from the following description and appended claims.